1. Field of the Invention
The present invention relates to an external body ventilator of the assistor-controller type, and more particularly relates to improved mechanisms for controlling the timing of artificial respiration in synchronism with the voluntary breathing movement of a patient connected to an external body ventilator.
2. Setting for the Invention
Although there are various types of artificial respiration devices, one popular device used by many is a positive-pressure type device which applies positive-pressure directly to the trachea. Using this device, it is possible to effect artificial respiration positively, i.e. by the direct introduction of air into and drawing of air from the lungs. However, with such a device, a tracheotomy is required. Naturally, this surgical procedure requires that the dissected portion of the trachea be disinfected in order to prevent infection, and in addition, there are several other drawbacks as well. In particular, the patient connected to such a device and having undergone such a surgical procedure is unable to consume solid food or engage in conversation with others.
Other prior art respiratory devices include external body ventilators, one of which is most commonly known as the "iron lung". The iron lung, however, is very large in scale and its efficiency is quite poor. Consequently, it has been used only rarely in recent years. Notably, the iron lung is a negative-pressure type device which effects inhalation and expiration of respiratory gases by way of providing an air-tight contained negative atmospheric pressure environment about a patient's chest, to cause the inflow and outflow of respiratory gases from the patient's respiratory system.
Another negative-pressure type device is the Cuirass ventilator which uses a jacket having a rigid shell that surrounds the chest portion of a patient. The jacket, when applied to the patient, is adapted to form an air-tight chamber between the patient's chest portion and the rigid shell. By reducing the air-tight chamber to a negative atmospheric pressure, artificial respiration is performed. In recent years, the advantages of this type of device have come to be recognized, since it does not require a tracheotomy of the patient, and also because it can be operated quite simply.
Among such external body ventilators, there is one in particular which employs an assistor-controller, as disclosed in Japanese Patent Laid open Application No. 176348/1986. According to this assistor-controller, when the patient is breathing voluntarily, artificial respiration can be performed in synchronism with the timing of a patient's voluntary breathing, and, when the patient ceases to breathe voluntarily, artificial respiration can be performed at a predetermined timing.
In the assistor-controller disclosed in Japanese Patent Laid open Application No. 176348/1986, the airway pressure, flow rate of respiration, the temperature of the nasal cavity of the patient, etc., have conventionally been used as biophysiological signals for purposes of detecting the timing of a patient's voluntary breathing. Using biophysiological signals of such quantitative parameters, the assistor-controller can be operated in synchronism with a patient's voluntary breathing.
However, such prior art methods and apparatus employing conventionally detected biophysiological signals described above are plagued with several significant shortcomings and drawbacks when the timing of voluntary breathing is determined on the basis of such signals. For example, in the case of a patient whose breathing movement is weak, as when a patient is suffering from myodystrophia, the signal to noise (S/N) ratio of conventionally detected biophysiological signals becomes extremely poor, possibly resulting in a malfunctioning of the apparatus.
Another principal drawback accompanying the use of conventional biophysiological signals is that such detective signals do not directly indicate the voluntary breathing movement of a patient, but rather are generated indirectly as a result of breathing. Thus, such biophysiological signals incur some time lag after the breathing movement and thus provide a source of error in efforts to synchronize the assistor-controller apparatus with the voluntary breathing movement of a patient.
In addition, conventionally detected biophysiological signals described above require that the sensors be installed on the patient. Consequently, it is often technically difficult to install on a patient a pressure sensor in the case of airway pressure detection, a flow rate sensor in the case of flow rate of respiration detection, and a temperature sensor in the case of nasal cavity temperature detection. Moreover, prior art biophysiological signal detection methods and apparatus are in general unpleasant to wear, and pose great discomfort to the patient as well.
Most significantly, however, using prior art biophysiological signal detection methods and apparatus, it is difficult to accurately synchronize the operation of artificial respiratory apparatus with a patient's voluntary breathing. Most importantly, prior art methods and apparatus have not provided an effective way of achieving such objectives in an accurate and also in a comfortable manner from the patient's viewpoint.
Accordingly, a primary object of the present invention is to provide a method of effecting artificial respiration and synchronism with a patient's voluntary breathing, utilizing principles of jaw movement detection, thereby overcoming the above-described shortcomings and drawbacks of prior art methodologies.
A further object of the present invention is to provide such a method while employing a negative-pressure generation means capable of effecting synchronus artificial respiration when the patient is breathing voluntarily, and effecting artificial respiration at a predetermined rate when the patient has stopped voluntary breathing.
An even further object of the present invention is to provide such a method utilizing an acceleration pick up installed on the jaw of a patient, for producing a signal corresponding to the change in velocity of the patient's jaw during breathing movements. Such signal detection is used for determining a timing corresponding to the voluntary breathing of the patient.
A further object of the present invention is to provide apparatus for effecting artificial respiration in synchronism with voluntary breathing of a patient, utilizing jaw movement detection.
Other and further objects of the present invention will be explained hereinafter, and will be more particularly delineated in the appended claims, and other objects of the present invention will hereinafter become apparent to one with ordinary skill in the art to which the present invention pertains.